In the context of the present invention the term “hearing device” refers to hearing aids (alternatively called hearing instruments or hearing prostheses) used to compensate hearing impairments of hard of hearing persons as well as audio and communication devices used to provide sound signals to persons with normal hearing capability, e.g. in order to improve hearing in harsh acoustic surroundings. Moreover, it also encompasses ear-level hearing protection devices, which safeguard a user from damaging his sense of hearing when subjected to severe acoustic shock events such as for instance gunfire or when exposed to excessive noise or sound levels for prolonged periods of time. Combinations of the mentioned devices such as for example hearing protection devices including a communication capability are also regarded as hearing devices in connection with the present invention.
Known hearing devices of the type which are at least partially worn within an ear canal of a user comprise a shell which is adapted to the individual shape of the user's ear canal. Such hearing devices are available in different styles, for instance as in-the-ear (ITE), including in-the-canal (ITC) and completely-in-canal (CIC), as well as hybrid behind-the-ear/in-the-ear type hearing devices. In the latter case the hearing device consists of a component to be worn “behind the ear” (BTE, i.e. behind the pinna) and a component to be worn at least partially within the “ear” (i.e. within the ear canal), whereby the ITE component contains a receiver and the BTE component contains an amplifier along with the necessary signal processing circuitry. ITE type hearing devices comprise a microphone and a receiver, a battery, an electronics module and one or more user control elements. These components are housed in a custom shell shaped according to a portion of the user's ear canal, whereby the microphone and user control element(s) are arranged at a face-plate further comprising a battery door. The face-plate is affixed to the distal end of the shell, whereas the receiver is positioned at the proximal end and is connected, typically by means of an acoustic tube, to the sound opening of the shell facing towards the ear drum when the hearing device is being worn in the ear canal. Conventionally, the sound opening is covered by a wax protection member in order to prevent soiling of the receiver, for instance due to ear wax or sweat.
There are a number of problems associated with such ITE type hearing devices. Due to the limited cross-section of and the bends in the ear canal there is an acute lack of space within the shell to position the necessary components, especially the bulky receiver as well as for instance an additional “ear canal microphone” intended to pick up the sound emitted into the ear canal by the receiver (not to be confused with the one or more “ambient microphones” which pick up the sound from the surroundings of the hearing device user). In order to provide a high output sound pressure level larger receivers are required, and their increased size significantly limits the possible insertion depth of the hearing device into the ear canal. Moreover, the acoustic coupling of the receiver to the ear canal considerably depends on the acoustic tubing extending from the sound output port of the receiver to the proximal sound opening of the shell. The length of this tubing depends on the final position of the receiver within the shell, which is determined by the way in which all the components can be manually arranged within the limited space inside the shell by the person who individually assembles the hearing device. During the assembly process the electronics module to which the receiver is connected is inserted through a distal opening in the shell. In order to allow access with minimal obstruction and permit flexible positioning no seatings are provided within the shell for the various components. As a consequence the stated acoustic tubing also acts as a suspension for the receiver. Once positioned excess tubing extending beyond the proximal sound opening of the shell is simply cut off. In summary the “fit rate” of a custom hearing device (i.e. the probability that a certain user can be provided with a specific hearing device that meets his needs) is significantly limited in state of the art ITE hearing devices. This limitation becomes even more pronounced with the advent of ear canal microphones being used to measure the sound emitted by the receiver into the ear canal and for instance to determine the sound pressure level at the user's ear drum. Moreover, the acoustic coupling between the receiver and the ear canal and properties of the mechanical suspension of the receiver are not known due to the way in which state of the art ITE hearing devices are assembled. This reduces the performance achievable by such hearing devices, e.g. in terms of feedback or occlusion (for instance when active occlusion cancellation is being employed).
In an attempt to simplify the manufacturing of ITE hearing devices EP-A 1 287 721 provides a method of producing an ITE hearing device whereby a transducer arrangement is introduced from the end forming the acoustic output of the hearing device housing. The proposed method allows assembly of the transducer arrangement into the hearing device in an automated manner.